EP3169505B1 - Measuring device and method for measuring test objects - Google Patents

Description

The invention relates to a measuring device and a method for measuring test objects. The test objects to be measured have, in particular at least in sections, at least one hollow-rectangular or hollow-cylindrical material layer.

Known measuring devices and methods for measuring test objects for tubes with a cylindrical or rectangular cross-section are generally based on X-ray or ultrasound technology. Typical x-ray based wall thickness measuring systems use two x-ray sources and two line detectors. In a full examination of wall and layer thicknesses by means of ultrasound technology, several transmitter-receiver units are generally used, which are to be arranged concentrically around a cylindrical test object, so that the ultrasound is incident radially on the tube and generates several measurement points. In addition to the X-ray and ultrasound-based systems, wall thickness measuring systems based on terahertz (THz) technology are becoming increasingly important. THz radiation is electromagnetic radiation in the frequency range of 0.1 to 10 THz.

The invention has for its object to provide a measuring device that allows the measurement of test objects with at least one at least partially hollow rectangular or hollow cylindrical material layer in a simple and flexible manner. In particular, the design of the measuring device is to be simplified, saves space and a component cost can be reduced.

The DE 10 2011 078 539 A1 describes a method and apparatus for extending the illumination of a test object illuminated by a microwave electromagnetic signal emitted by a transmitter antenna. The microwave signal reflected by the test object is received by at least one receiving antenna. In this case, reflector elements are arranged aligned with respect to the test object, so that the reflected from the reflector element and the test object microwave signals are received in a receiving antenna, in addition to this microwave rays coming from a transmitter antenna without reflection on the reflector element on the test object, are received and used.

The US 2011/0112795 A1 describes a light-converging lens having a plurality of lenses arranged side by side, in particular also as a square, and surrounding a light-receiving element.

The WO 95/07471 A1 describes an optical system for detecting the presence and position of at least one stationary or moving object. Here, embodiments are shown with orthogonal arrangement of two mirrors and two Kollimationslinsen.

The US 2010/0079754 A1 shows an apparatus for Raman spectroscopy, wherein light concentrators are provided for condensing light and furthermore mirrors.

The Ep 2 752 287 A1 describes a device for measuring extrusion products, in particular pipes by means of THz radiation in transmission.

The DE 198 52 335 A1 describes a device for error detection and / or wall thickness measurement in continuous bands or pipes made of plastic by means of ultrasonic signals.
This object is achieved by a measuring device having the features of claim 1. The measuring device or reflection measuring device serves to carry out reflection measurements on the test object to be measured. The measuring device comprises a transmitter-receiver unit with a transmitter for emitting radiation in an xy plane from a beam spot and an associated receiver for detecting a radiation reflected at a test object. A first collimator-focusing arrangement of the measuring device has collimator-focusing elements for converting the emitted radiation into collimated radiation and for focusing the reflected radiation into the beam spot, the collimator-focusing elements being arranged such that two adjacent collimator-focusing Enclose an angle of substantially 90 ° in the xy plane so that the collimator focus elements form a collimator focus square. A common focus of the collimator-focusing elements lies in the xy-plane in the beam spot. The measuring device further comprises an xy-plane test object receiving area for placing the test object and at least one mirror array having mirror elements for deflecting the collimated radiation and the reflected radiation between the collimator-focusing array and the test object receiving area. The mirror elements are arranged such that two adjacent mirror elements in the xy plane enclose an angle of substantially 90 ° such that the mirror elements form a mirror rectangle, mirror surfaces of the mirror rectangle parallel to collimator Collimator Focusing Square Focusing Diagonals are. Furthermore, the measuring device has a control unit for evaluating the detected radiation.

Preferably, four collimator focusing elements are provided which form the collimator focusing square. Advantageously, four mirror elements are arranged in the x-y plane which form the mirror rectangle. Advantageously, the mirror rectangle is designed as a mirror square. The mirror surfaces of the mirror elements are preferably identical. In this case, the mirror surfaces are formed from a material that acts in particular for THz radiation as a nearly ideal mirror. As a material is electrically conductive material, such as aluminum or steel. It is advantageous if a surface flatness of the mirror surfaces is higher than one tenth of the shortest wavelength of the THz radiation used.

For measuring the test object, the transmitter of the transceiver unit first emits radiation in the direction of the collimator-focusing elements of the collimator-focusing arrangement. The emitted radiation is converted into collimated radiation by means of the collimator-focusing elements. The collimated radiation is deflected by means of the mirror elements into the test object receiving area and impinges on the test object. From the test object, the radiation is reflected. The test object is preferably arranged such that a central longitudinal axis of the test object runs perpendicular to the xy plane or parallel to a z direction. The emitted collimated radiation is incident perpendicular to a surface of the specimen, whereby the reflected radiation preferably travels along the same ray path in the opposite direction back to the beam spot where it is detected. The radiation reflected on the test object preferably has the same beam path, but in the opposite direction, as the incident radiation. The reflected radiation is deflected by the mirror elements to the collimator-focusing arrangement, where it is focused into the beam spot. The receiver detects the reflected radiation and passes the Measured values continue to the control unit, which evaluates the detected radiation or the measured values.

The measuring device according to the invention has a comparatively simple structure, since the transmitter-receiver unit can be arranged at a distance from the test object receiving area in the x-y plane due to the mirror arrangement. It is also possible to position the transceiver unit in the z-direction at a distance from the x-y plane. Both hollow-rectangular and hollow cylindrical test objects can be examined with the measuring device according to the invention. By pivoting or rotating the transmitter-receiver unit about a rotation axis passing through the steel point, a further peripheral region of the test object can be measured with only one transmitter-receiver unit. For example, it is possible to measure a thickness of at least one hollow-rectangular or hollow-cylindrical material layer over the entire circumference.

The test object is formed in particular from plastic and has a hollow-rectangular or hollow-cylindrical material layer or a plurality of hollow-rectangular or hollow-cylindrical material layers. The test object can be extruded parallel to the z-direction and measured during the extrusion.

The measuring device allows in particular the measurement of test objects made of plastic. The transmitter-receiver unit is preferably designed such that electromagnetic radiation with a frequency in the range from 0.01 THz to 50 THz, in particular from 0.05 THz to 20 THz, and in particular from 0.1 THz to 10 THz can be emitted or emitted . is detectable. The measurement of the test object by means of the radiation or THz radiation is based on the measurement of a transit time difference of the radiation which is reflected at the boundary layers. boundary layers are the surfaces of the test object, such as a tube outer wall and a tube inner wall, and contiguous material layers within the test object. The transmitter-receiver unit is in particular designed such that THz pulses can be emitted or detected.

The embodiment according to claim 3 leads to a simple construction of the measuring device.

The measuring device according to claim 4 is again particularly simple. The lenses may be converging lenses, by means of which the radiation emitted by the transmitter can be converted into collimated radiation. A common focus of the lenses lies in the beam spot of the transmitter. A lens diameter of the lenses preferably corresponds approximately to an edge length of the collimator-focusing square, depending on the lens shape. Furthermore, the reflected beam can be focused on the beam spot in a simple manner by the lenses of the collimator-focusing arrangement.

The embodiment according to claim 5 leads to a simple construction of the measuring device.

According to claim 6, the mirror arrangement is designed such that a first mirror element deflects the collimated radiation to a second mirror element, wherein the second mirror element deflects the radiation onto the Prüfobjektaufnahmebereich. Conversely, analogously, the second mirror element deflects the radiation reflected at the test object onto the first mirror element, wherein the first mirror element deflects the radiation onto the collimator-focusing arrangement.

A measuring device according to claim 7 ensures in a structurally particularly simple way that the collimated radiation is deflected twice at the mirror arrangement.

By a measuring device according to claim 8, the measurement of the test object over its entire circumference is made possible. The fact that the transmitter-receiver unit is designed such that the emitted radiation is rotatable in an x-y plane around the beam point ensures that a defined test area can be scanned on the test object by each beam emitted at an emission angle.

A measuring device according to claim 9 represents a structurally particularly simple design. A component expenditure of the measuring device is kept low.

By a measuring device according to claim 10, a permanently stable and reliable connection of optical and electrical signals is ensured. It is advantageous if the transmitter and the receiver of the transceiver unit are immovably positioned outside the x-y plane. The radiation emitted by the transmitter is along the z-direction, which is perpendicular to the x-y plane. The emitted radiation can be deflected in the beam spot by the rotation mirror to the collimator-focusing arrangement. The rotation axis of the rotation mirror is parallel to the z-direction. Preferably, it is achieved by the rotation mirror that the emitted radiation rotates through 360 °. The provision of a rotational mirror achieves a stable and extremely space-saving design of the measuring device in the x-y plane.

A measuring device according to claim 11 allows an arrangement of the transmitter and the receiver along the z-direction. Such a measuring device ensures a simple and space-saving way Measurement of the test object. The fact that the transmitter and the receiver are arranged along the z-direction, ie perpendicularly spaced from the xy plane, the area bounded by the collimator-focusing arrangement and the mirror arrangement is not unnecessarily affected by the transmitter and the receiver , The rotation mirror requires a comparatively small space requirement, so that the transceiver unit in the xy plane is extremely compact. The z-direction or z-axis is perpendicular to the xy-plane. Accordingly, the rotation mirror is inclined by 45 ° to the xy plane for deflecting the emitted radiation.

A measuring device according to claim 12 makes it possible to measure tubes with a circular-cylindrical cross-section in a particularly simple way over the entire circumference. The second collimator-focusing arrangement serves to focus the collimated radiation into a common test object focus and to convert the reflected radiation into reflected collimated radiation. The collimator-focusing elements of the collimator-focusing arrangement are designed such that they transform the collimated radiation so that it is incident perpendicular to a surface of the test object.

A measuring device according to claim 13 allows in a structurally simple manner that the collimated radiation deflected by the mirror arrangement is incident perpendicularly on a surface of the test object.

A measuring device according to claim 14 optimizes the course of the emitted and reflected radiation. Furthermore, the available space is optimally utilized.

The invention is further based on the object to provide a method which in a simple and flexible way, the measurement of test objects allows. In particular, the method is intended to enable the measurement of test objects which, at least in sections, have at least one hollow-rectangular or hollow-cylindrical material layer.

This object is further achieved by a method having the features of independent claim 16. The advantages of the method according to the invention correspond to the already described advantages of the measuring device according to the invention. In particular, the method according to the invention can also be combined with the features of the device claims, i. in particular, claims 1 to 15 are further developed. Accordingly, the measuring device according to claims 1 to 15 can be characterized by the features of the method claims, i. in particular claims 16 to 19, further developed. In this case, the device and the method allow, in particular, also a layer thickness and wall thickness measurement of plastic objects such as pipes, in particular by transit time measurement.

With the method according to the invention, it is possible to determine both the layer and wall thicknesses of a pipe with a rectangular cross-section and the layer and wall thicknesses of a cylindrical tube. In rectangular tubes, the emitted radiation is incident perpendicular to the surface of the test object. Accordingly, in tubes of cylindrical cross section, each defined test area of the cross-sectional surface is scanned with radially incident, emitted radiation. In both design variants of the test object, only one transmitter-receiver unit is necessary in each case.

A method according to claim 17 ensures a full measurement of the test object. Either the transmitter-receiver unit as a whole rotates in the beam spot about the rotation axis or a rotation mirror. The rotation scans a defined test area on the test object through each beam emitted at an emission angle. As a result, only a transmitter-receiver unit is necessary to scan the entire circumference of a rectangular or hollow cylindrical test object. The mirror arrangement redirects the rotating, collimated radiation between the collimator focus assembly and the test object receiving area. This allows a measurement of the test object inline in the manufacturing process. In the manufacturing process, the test object itself is usually not pivotable about its central longitudinal axis or rotatable.

A measuring device according to claim 18 ensures reliable and accurate measurement results.

In the event that test objects in the form of a cylindrical tube are to be tested by means of the method according to the invention, the radiation emitted and deflected by the mirror arrangement is focused by a second collimator-focusing arrangement and directed onto the test object. The focal point coincides with the test object focus or center. Thus, it is possible for each point of the incident wavefront of a beam pulse to hit simultaneously and perpendicularly to the test object arranged concentrically with the test object focal point and extruded parallel to the z direction. As a result, the radiation is always ideally reflected regardless of a diameter of the test object. Due to the fact that the radiation impinges radially or perpendicularly on the surface of the test objects, a high measuring accuracy is achieved.

Fig. 1

eine Draufsicht auf eine Messvorrichtung zur Vermessung eines Prüfobjekts gemäß einem ersten Ausführungsbeispiel,

Fig. 2

eine Ansicht der Messvorrichtung gemäß Fig. 1, wobei in einem Prüfobjektaufnahmebereich ein Prüfobjekt mit hohlrechteckförmigem Querschnitt angeordnet ist,

Fig. 3

eine Draufsicht auf eine Messvorrichtung zur Vermessung eines Prüfobjekts gemäß einem zweiten Ausführungsbeispiel,

Fig.4

eine auf Fig. 2 basierende Ansicht der ersten Ausführungsvariante der Messvorrichtung, wobei eine reale Strahlausbreitung dargestellt ist,

Fig. 5

eine auf Fig. 3 basierende Darstellung der zweiten Ausführungsvariante der Messvorrichtung, wobei eine reale Strahlenausbreitung dargestellt ist,

Fig. 6

eine Ansicht der zweiten Ausführungsvariante der Messvorrichtung gemäß Fig. 3 und Fig. 5, wobei eine Aufspaltung und Ausbreitung eines divergenten Strahls gezeigt ist,

Fig. 7

eine erste Ausführungsvariante einer Sender-Empfänger-Einheit einer der Messvorrichtungen der Fig. 1 bis Fig. 6,

Fig. 8

eine zweite Ausführungsvariante einer Sender-Empfänger-Einheit einer der Messvorrichtungen der Fig. 1 bis Fig. 6, und

Fig. 9

eine Draufsicht auf eine Messvorrichtung zur Vermessung eines Prüfobjekts gemäß einem dritten Ausführungsbeispiel.

Further features, advantages and details of the invention will become apparent from the following description of several embodiments. Show it:

Fig. 1

a top view of a measuring device for measuring a test object according to a first embodiment,

Fig. 2

a view of the measuring device according to Fig. 1 in which a test object with a hollow-rectangular cross-section is arranged in a test object receiving area,

Fig. 3

a top view of a measuring device for measuring a test object according to a second embodiment,

Figure 4

one on Fig. 2 based view of the first embodiment of the measuring device, wherein a real beam propagation is shown,

Fig. 5

one on Fig. 3 based representation of the second embodiment of the measuring device, wherein a real beam propagation is shown,

Fig. 6

a view of the second embodiment of the measuring device according to Fig. 3 and Fig. 5 showing a splitting and spreading of a divergent beam,

Fig. 7

a first embodiment of a transmitter-receiver unit of one of the measuring devices of Fig. 1 to Fig. 6 .

Fig. 8

a second embodiment of a transmitter-receiver unit of the measuring devices of Fig. 1 to Fig. 6 , and

Fig. 9

a plan view of a measuring device for measuring a test object according to a third embodiment.

The following is based on Fig. 1 and Fig. 2 a first embodiment of the invention described. For measuring a test object 2, a measuring device 1 has a transmitter-receiver unit 3, a first collimator-focusing arrangement 4, a mirror arrangement 5, a test object receiving area 6 and a control unit 7.

The measuring device 1 according to the Fig. 1 and Fig. 2 is used in particular for the measurement of test objects 2 with a rectangular cross-section. The test object 2, which in Fig. 2 is shown, has a hollow-rectangular contour.

For clarity, is in Fig. 1 and Fig. 2 no transmitter-receiver unit shown. In the embodiment shown according to Fig. 1 and Fig. 2 the measuring device 1 finds the transmitter-receiver unit 3 according to Fig. 7 Application. Alternatively, it is also possible to use the transceiver unit 3a according to FIG Fig. 8 apply in the measuring device 1, without the basic operation of the measuring device 1 changes. FIGS. 7 and 8 show in detail possible embodiments of the transmitter-receiver unit 3 and 3a.

Both embodiments of the transceiver unit 3 and 3a each include a transmitter 9 for emitting radiation S in an xy plane E _xy starting from a beam spot SP. The emitted radiation is denoted by S from the transmitter 9 to the test object 2 below. The radiation reflected on the test object 2 is subsequently designated by the test object 2 to a receiver 10 by R. The receiver 10 is used to detect the reflected on the test object 2 Radiation R. To measure the test object 2, the detected radiation R is evaluated by means of the control unit 7.

In the embodiment of the transmitter-receiver unit 3 according to Fig. 7 For example, the transmitter 9 and the receiver 10 are arranged in a z-direction at a distance from the xy plane E _xy . The transmitter 9 and the receiver 10 are arranged along a first z-axis Z ₁ , which runs parallel to the z-direction through the beam spot SP. The transmitter-receiver unit 3 is designed such that the emitted radiation R in the xy plane E _xy is rotatable about the beam spot SP. For this purpose, the transmitter-receiver unit 3 has a rotation mirror 11 which is rotatable about an axis of rotation 12 perpendicular to the xy plane E _xy through the beam spot SP. The axis of rotation 12 coincides with the first z-axis Z ₁ . The rotation mirror 11 is tilted by a tilt angle α _κ of 45 ° with respect to the xy plane E _xy . The rotational movement of the rotary mirror 11 about the axis of rotation 12 is advantageously a continuous rotational movement along a direction of rotation. The direction of rotation is in Fig. 7 illustrated by the directional arrow 13.

The transmitter 9 and the receiver 10 are in the embodiment shown, the transmitter-receiver unit 3 according to Fig. 7 immovable. The radiation S emitted by the transmitter 9 is focused from the z-direction coming by means of a focusing means 8 on the beam spot SP. The rotation mirror 11 directs the radiation S coming from the z direction into the xy plane E _xy , the radiation S rotating through the rotation mirror 11 through 360 ° about the rotation axis 12. This structure of the transceiver unit 3 is easy to implement, stable and takes up little space, so that constructions with small maximum diameters of the test object 2 can be implemented. For measuring the test object 2, the transmitter-receiver unit 3 is designed such that the electromagnetic radiation S, R having a frequency in the range of 0.01 THz to 50 THz, in particular from 0.05 THz to 20 THz, and in particular from 0.1 THz to 10 THz can be emitted or detected. The radiation S is preferably emitted in pulsed form, that is to say generates THz pulses.

According to the alternative embodiment of the transmitter-receiver unit 3a according to Fig. 8 is in contrast to the transmitter-receiver unit 3 after Fig. 7 no rotation mirror provided. The transmitter-receiver unit 3a is designed such that it is rotatable as a whole about the axis of rotation 12 in the beam spot SP. The transmitter 9 and the receiver 10 are thus movable. The rotational movement of the transmitter-receiver unit 3a about the axis of rotation 12 is advantageously a continuous rotational movement along the direction of rotation 13. For connecting optical and electrical signals to the transceiver unit 3a, a rotary coupling, not shown, is provided.

Both embodiments of the transmitter-receiver units 3, 3a can be used in the measuring device 1 according to the invention without the functioning of the measuring device 1 according to the invention changing.

The first collimator-focusing arrangement 4 comprises collimator-focusing elements 14, 15, 16, 17 for converting the emitted radiation S into collimated radiation S and for focusing the reflected radiation R into the beam spot SP. In the embodiment of the measuring device 1 according to FIGS Fig. 1 and Fig. 2 four collimator focusing elements 14, 15, 16, 17 are provided. The collimator-focusing elements 14, 15, 16, 17 are arranged such that in each case two adjacent collimator-focusing elements 14, 15, 16, 17 in the xy plane E _xy include an angle α _KF of 90 °, so the collimator focusing elements 14, 15, 16, 17 in the xy plane E _xy a collimator-focusing square 18 form. Due to the square shape, the first collimator-focusing arrangement 4 comprises a first collimator-focusing diagonal 28 and a second collimator-focusing diagonal 29.

The collimator focusing elements 14, 15, 16, 17 are formed as lenses. For the sake of simplicity, with regard to the measuring device 1, the collimator-focusing elements 14, 15, 16, 17 are therefore referred to as lenses.

The lenses 14, 15, 16, 17 are each arranged in the beam path between the beam spot SP and the mirror arrangement 5. The incident emitted radiation S is collimated by means of the lenses 14, 15, 16, 17 in the xy-plane E _xy . In concrete terms, this means that the beam paths emitted in one quadrant of the collimator-focusing square 18 run parallel to one another after the lenses 14, 15, 16, 17. As a result of the rotation of the emitted radiation S in the xy plane E _xy about the axis of rotation 12, beam paths can be emitted in each quadrant of the collimator-focusing square and can be collimated by the lenses 14, 15, 16, 17.

The lenses 14, 15, 16, 17 are identical in shape and size. A common focus B _{1 of} the lenses in the xy plane E _xy lies in the beam spot SP. For this purpose, the lenses 14, 15, 16, 17 are formed as plano-convex converging lenses whose convex curvature is directed in each case in the direction beam spot SP. The planar sides of the lenses 14, 15, 16, 17 form edges of the collimator-focusing square 18.

In the embodiment shown, the lenses 14, 15, 16, 17 each have the numerical aperture 0.71. A lens diameter of the lenses 14, 15, 16, 17 in the embodiment shown is 2f, where f a focal length of the lenses 14, 15, 16, 17. Thus, the collimator focus square has 18 edge lengths of 2f.

In the variant embodiment shown, the mirror arrangement 5 comprises four mirror elements 19, 20, 21, 22 for deflecting the emitted collimated radiation S and the reflected radiation R between the collimator-focusing arrangement 4 and the test object receiving area 6. The test object receiving area 6 Arrangement of the test object 2 lies in the xy plane E _xy . The mirror elements 19, 20, 21, 22 are arranged such that two adjacent mirror elements 19, 20, 21, 22 enclose an angle α _SE of 90 °, so that the mirror elements 19, 20, 21, 22 in FIG the xy plane E _{xy form} a mirror rectangle 23. In the embodiment of the measuring device 1 according to the Fig. 1 and Fig. 2 the mirror rectangle 23 is formed as a mirror square, wherein the mirror elements 19, 20, 21, 22 are identical in shape and size. In the embodiment shown, the mirror rectangle 23 has edge lengths of $4\sqrt{2}\mathrm{f},$

How out Fig. 1 and Fig. 2 Clearly, the mirror rectangle 23 surrounds the collimator focus square 18 in the xy plane E _xy . Mirror surfaces 24, 25, 26, 27 of the mirror elements 19, 20, 21, 22 are arranged parallel to the collimator-focusing diagonals 28, 29 of the collimator-focusing square 18.

After collimation of the emitted radiation S by the collimator-focusing arrangement 4, the design of the mirror arrangement 5 allows each beam path of the collimated radiation S to be reflected twice. For this purpose, the mirror arrangement 5 is designed such that a first of the mirror elements 19, 20, 21, 22 deflects the collimated radiation S onto a second of the mirror elements 19, 20, 21, 22, the second mirror unit Elements 19, 20, 21, 22 the radiation S deflects to the Prüfobjektaufnahmebereich 6. The mirror arrangement 5 is further embodied in such a way that the collimated radiation S impinges on the respective first and second mirror elements 19, 20, 21, 22 at an angle of incidence _{.alpha..sub.IN} of substantially 45.degree. Through which mirror elements 19, 20, 21, 22 a deflection of the collimated radiation S takes place depends on which quadrant of the collimator-focusing square 18 the radiation S was emitted.

In the embodiment according to Fig. 1 and Fig. 2 For example, the second mirror surface 25 and the fourth mirror surface 27 are arranged parallel to each other and symmetrically with respect to the first collimator focusing diagonal 28. Accordingly, the first mirror surface 24 and the third mirror surface 26 are arranged parallel to each other and symmetrically with respect to the second collimator focusing diagonal 29. The first collimator focusing diagonal 28 also coincides with a side bisector 33 of the mirror square 23 formed as a mirror square. Furthermore, a lens edge 30 formed by the first lens 14 and the second lens 15 adjoins the first mirror surface 24.

The measuring device 1 is designed in such a way that the collimated radiation S reaches the test object receiving region 6 after the reflections on the mirror arrangement 5. The test object receiving area 6 extends in the xy plane E _xy in the form of a test object receiving square 31. An edge length of the test object receiving square 31 corresponds to the edge length of the collimator focusing square 18 and corresponds to twice the focal length f of the lenses 14, 15, 16, 17. A first inspection object shot square diagonal 32 coincides with the same side bisector 33 of the mirror rectangle 23 as the first collimator focusing diagonal 28. The inspection object receiving square 31 and the collimator focusing square 18 are along the Side bisecting 33 arranged adjacent to each other and fill them out exactly. This means a sum of the lengths of the first inspection object receiving square diagonal 32 and the first collimating focusing diagonal 28 corresponds to a length of the side bisector 33 of the mirror rectangle 23.

As in Fig. 2 illustrates, the test object 2 is arranged for measurement within the Prüfobjektaufnahme square 31. To be detected profile walls 34 of the hollow rectangular test object 2 are aligned parallel to the edges of the Prüfobjektaufnahme-square 31. This allows the collimated radiation S to be incident perpendicular to the profile walls 34 and the reflected radiation R to travel along the same optical path in the opposite direction back to the beam spot SP, where it is detectable by the receiver 10. The test object receiving square 31 represents a maximum detection range. If a profile cross section of a test object 2 is completely in the test object receiving square 31, all profile walls which run parallel to edges of the test object receiving square 31 can be tested in their entirety.

• Der Sender 9 emittiert Strahlung S in Form von THz-Pulsen. Die Erzeugung von THz-Pulsen ist grundsätzlich bekannt. THz-Pulse werden beispielsweise optisch mittels Femtosekunden-Laserpulsen und photoleitenden Schaltern erzeugt. Wie vorab unter Bezug auf Fig. 7 beschrieben, wird die Strahlung S in der z-Richtung emittiert und auf den Rotations-Spiegel 11 fokussiert.

The operation of the measuring device 1 is as follows:

• The transmitter 9 emits radiation S in the form of THz pulses. The generation of THz pulses is basically known. THz pulses are generated, for example, optically by means of femtosecond laser pulses and photoconductive switches. As in advance with reference to Fig. 7 described, the radiation S is emitted in the z-direction and focused on the rotation mirror 11.

By rotation of the rotational mirror 11 about the axis of rotation 12 it is achieved that the emitted radiation S in the xy plane E _xy rotates about the beam spot SP. Each beam emitted at a certain emission angle α _E scans a defined test area on the test object 2. Exemplary are in Fig. 1 and Fig. 2 with solid lines ideal rays drawn. On a real ray propagation will be later with respect to Fig. 4 . Fig. 5 and Fig. 6 received.

The entirety of the radiation generated by rotation and expiring successively from the beam spot SP can be subdivided into four beam bundles with an opening angle ao of 90 ° each. Each bundle of rays is assigned a quadrant of the collimator-focusing square 18.

In a first step, the divergent radiation emanating from the beam spot SP is collimated by means of the lenses 14, 15, 16, 17 of the first collimator-focusing arrangement 4. After the lenses 14, 15, 16, 17, all rays emitted in one quadrant of the collimator-focusing square 18 are parallel to one another. This results in four collimated beam paths.

After collimation by the collimator-focusing arrangement 4, each beam is reflected twice by the mirror arrangement 5. The collimated radiation S impinges on the respective mirror element 19, 20, 21, 22 at the angle of incidence α _IN of 45 °.

By way of example, the radiation collimated by the third lens 16 impinges on the second mirror element 20 at the angle of incidence α _IN of 45 °, where it is reflected by the second mirror surface 25 to the third mirror element 21, where the collimated radiation S again impinges at the angle of incidence _αIN of 45 °. The third mirror surface 26 forwards the collimated radiation S to the test object receiving region 6.

After the reflections, the collimated radiation S impinges perpendicular to the profile walls 34 of the test object 2. By the design of the measuring device 1, the THz pulses from the transmitter-receiver unit 3 are thus radiated perpendicular to the test object 2.

As described above, an emission direction of the radiation S emanating from the beam spot SP is varied by rotation of the rotation mirror 11. In Fig. 1 and Fig. 2 a rotation of the emitted radiation S in the direction of rotation 13 is shown. One after the other, so different beam paths, wherein the profile walls 34 of the test object 2 in the direction of rotation 13 are scanned sequentially completely around the beam spot SP. The individual profile walls 34 of the test object 2 are checked one after the other. Along the respective profile wall 34, however, a direction of movement of the radiation S runs counter to the direction of rotation 13, which is in particular Fig. 2 is apparent.

The test object 2 is to be arranged such that its central longitudinal axis 35 extends along a second z-axis Z ₂ through the xy plane E _xy in the test object receiving region 6 and an extrusion direction of the test object 2 is parallel to the z-axis.

The radiation R reflected on the test object 2 or the reflected THz pulses travel at least partially along the same beam paths back to the transceiver unit 3. The reflected radiation R is reflected twice again by means of the mirror arrangement 5 and in the direction of the receiver 10 diverted. The collimator-focusing arrangement 4 focuses the reflected radiation R at the common focus B _{1 of} the first collimator-focusing arrangement 4. The receiver 10 detects the focused radiation R. The structure of the receiver 10 is basically known. THz pulses are detected, for example, by optical sampling with femtosecond laser pulses. The detected radiation R is evaluated by the control unit 7.

By means of the measuring device 1 according to the invention, the hollow-rectangular test object 2 can be scanned in its entirety and measured, without any need for a rotation of the test object 2 about its central longitudinal axis 35 or a translational movement of the test object. This is particularly advantageous if a measurement of the test object 2 takes place during an extrusion process. A measurement of the test object 2 can therefore be done inline. A full measurement of the test object 2 can be achieved with only one transmitter-receiver unit 3.

In Fig. 4 Furthermore, a real beam propagation of the radiation S, R is shown. The radiation S is emitted as described above by means of the transmitter-receiver unit 3. The emitted radiation S has a beam divergence. The radiation S, R has a divergence angle Δα _R in the xy plane E _xy . Due to the divergence angle Δα _R , the radiation S which impinges on the lenses 14, 15, 16, 17 is adjustable and thus also a diameter of the collimated radiation S. The collimated radiation S does not strike the test object 2 punctually in the case of a real beam propagation. but in a measuring range. The size of the measuring range depends on the divergence angle Δα _R. Despite the divergent beam propagation, the radiation S or the respective THz pulse impinges perpendicularly on the profile walls 34 of the test object 2, and at the same points in time. This ensures that the reflected radiation R has a high signal quality and in particular the reflected THz pulses are not washed out and are attenuated in their amplitude.

The following is based on Fig. 3 A second embodiment of the invention described. In contrast to the measuring device 1 of the first embodiment variant, the measuring device 1a is used in particular for measuring test objects 2a with a hollow-cylindrical cross-section. Components of the measuring device 1a, which with parts of the first embodiment the measuring device 1 are identical, the same reference numerals.

The transmitter-receiver unit 3, the first collimator-focusing arrangement 4 and the mirror arrangement 5 of the measuring device 1a are identical to the measuring device 1. In contrast to the first embodiment, the measuring device 1a comprises a second collimator-focusing arrangement 37 for Focusing the radiation S collimated by means of the first collimator-focusing arrangement 4 into a common test object focal point B ₂ and for converting the reflected radiation R into reflected collimated radiation R.

The second collimator focusing arrangement 37 is arranged in the test object receiving area 6 concentrically with the test object focal point B ₂ . The second collimator-focusing arrangement 37 is formed identically to the first collimator-focusing arrangement 4 and comprises four collimator-focusing elements formed as plano-convex lenses 14a, 15a, 16a, 17a. Similarly, the lenses 14a, 15a, 16a, 17a of the second collimator focus assembly 37 also form a collimator focus square 18a. The collimator focus square 18a includes a first collimator focus diagonal 28a and a second collimator focus diagonal 29a. The second collimator focusing arrangement 37 is arranged in the test object receiving area 6 in such a way that the first collimator focusing diagonal 28a of the second collimator focusing arrangement 37 coincides with the side bisector 33 of the square mirror rectangle 23. Put simply, the second collimator-focusing arrangement 37 in the xy plane E _{xy is} congruent with that associated with FIG Fig. 1 and Fig. 2 Test object receiving square 31 described formed.

• Nach Bereitstellung der Messvorrichtung 1a wird das hohlzylinderförmige, als Rohr ausgebildete Prüfobjekt 2a derart im Prüfobjektaufnahmebereich 6 angeordnet, dass eine Mittellängsachse 35a durch den Prüfobjekt-Brennpunkt B₂ läuft und eine Extrusionsrichtung des Prüfobjekts 2a parallel zur z-Achse ist bzw. senkrecht zur x-y-Ebene E_xy. Anschließend wird wie vorab im Zusammenhang mit Fig. 1 und Fig. 2 beschrieben, rotierende THz-Strahlung S durch den Sender 9 emittiert und durch die erste Kollimator-Fokussier-Anordnung 4 kollimiert. Anschließend wird mittels der Spiegel-Anordnung 5 die kollimierte Strahlung S zum Prüfobjektaufnahmebereich 6 umgelenkt. Die senkrecht auf die Linsen 14a, 15a, 16a, 17a einfallende Strahlung S wird durch die zweite Kollimator-Fokussier-Anordnung 37 auf den Prüfobjekt-Brennpunkt B₂ fokussiert. Dies hat zur Folge, dass die THz-Strahlung S senkrecht zur Oberfläche des hohlzylinderförmigen Prüfobjekts 2a, also radial zur selbigen einfällt. Dies ermöglicht, dass die reflektierte Strahlung R entlang der gleichen Strahlengänge in entgegengesetzter Richtung zurück zum Strahlpunkt SP läuft, wo sie durch den Empfänger 10 detektiert wird.

The operation of the measuring device 1a is as follows:

• After provision of the measuring device 1a, the hollow cylindrical test object 2a designed as a tube is arranged in the test object receiving region 6 such that a central longitudinal axis 35a passes through the test object focal point B ₂ and an extrusion direction of the test object 2a is parallel to the z axis or perpendicular to the xy axis. Level E _xy . Subsequently, as related in advance Fig. 1 and Fig. 2 described rotating THz radiation S emitted by the transmitter 9 and collimated by the first collimator-focusing arrangement 4. Subsequently, by means of the mirror arrangement 5, the collimated radiation S is deflected to the test object receiving area 6. The radiation S incident perpendicular to the lenses 14a, 15a, 16a, 17a is focused by the second collimator-focusing arrangement 37 onto the test object focal point B ₂ . This has the consequence that the THz radiation S perpendicular to the surface of the hollow cylindrical test object 2a, that is incident radially to the same. This allows the reflected radiation R to travel along the same beam path in the opposite direction back to the beam spot SP where it is detected by the receiver 10.

In the embodiment of the measuring device 1a shown, a maximum detectable pipe diameter of the test object 2a is 2 (f-p) where p denotes a maximum thickness of the lenses 14a, 15a, 16a, 17a. Ideally, the lens thickness p is significantly smaller than the focal length f.

In Fig. 5 and Fig. 6 Furthermore, a real beam propagation of the radiation S, R in connection with the second embodiment of the measuring device 1a is shown. As explained, as part of the measurement of the hollow cylindrical test object 2a, the collimated THz radiation S is focused through the lenses 14a, 15a, 16a, 17a and directed to the test object 2a. However, a focal point is not on the test object 2a but in the test object focal point B ₂ . As a result, every point of an incident hits Wavefront of a THz pulse at the same time and perpendicular to the concentric to the test object focus B ₂ arranged test object 2a. As a result, the THz radiation S is always ideally reflected independently of a pipe diameter. Thus, a detection geometry is optimally designed for a geometry of the test object 2a. The radiation S incident on the test object focal point B ₂ and the radiation S emanating from the beam spot SP have the same divergence angle Δα _R , the divergence angle Δα _{R being} independent of a radiation direction.

In Fig. 6 the measuring device 1a is shown, wherein emitted radiation S strikes an edge of the collimator-focusing square 18, at which the fourth lens 17 and the first lens 14 coincide to form the angle α _KF of 90 °. The considered radiation S thus impinges on two lenses 14, 17 and is split, so that partial radiations S1 and S2 are formed, which form two measuring ranges on the test object 2a. As Fig. 6 can be seen in this particular case, two nearly opposite areas of the test object 2a are scanned. A measurement signal is thus composed of reflections in these two areas. A superposition of the measurement signals provides information about the positioning of the test object 2a in the structure. If the reflections coincide, the test object 2a is centered. If the reflections do not coincide, one of the measuring ranges is closer to one of the lenses 14a, 15a, 16a, 17a. As the THz beam S passes over the corner of the collimator focus square 18, the ratio of the strength of the two reflections changes in successive measurements. Thus, each of the two signal components can be uniquely attributed to the reflection from a region.

The following is based on Fig. 9 A third embodiment of the invention described. A measuring device 1b according to the third embodiment differs from the measuring devices 1, 1a primarily by the design of a mirror assembly 39 from. The mirror arrangement 39 is rectangular in shape as a mirror rectangle 40. The mirror rectangle 40 comprises four mirror elements 41, 42, 43, 44, which together form the mirror rectangle 40. In addition, the mirror arrangement 39 comprises a fifth mirror element 45, which is arranged within the mirror rectangle 40. The mutually opposite mirror elements 41, 43 are identical in shape and size. Accordingly, the opposing mirror elements 42, 44 are identical in shape and size. However, the mirror elements 41, 43 differ in edge length from the mirror elements 42, 44. The fifth mirror element 45 extends parallel to the mirror elements 42, 44 between them. In the structure according to Fig. 9 For example, the radiation S between the first collimator focusing arrangement 4 and the inspection object receiving area 6 is reflected three times. In this case, a length of the beam path 10f. With regard to the further structure and further operation, reference is made to the first embodiment.

In principle, it is also conceivable in further alternative embodiments to provide more than two or three reflections between first collimator-focusing arrangement 4 and test object receiving area 6. Furthermore, it is also possible in principle for the first collimator-focusing arrangement 4 and / or the second collimator-focusing arrangement 37 to be designed as collimator-focusing polygons having more than four corners. However, a majority of test objects to be measured has edges that are perpendicular to each other. Therefore, in particular, the embodiments of the measuring device 1 and the measuring device 1b form preferred solutions.

Claims (19)

1. Measuring device for measuring test objects having

   - a transmitter-receiver unit (3; 3a) having

   - a transmitter (9) for emitting terahertz radiation (S) in an x-y plane (E_xy) starting from a beam point (SP) and

   - an associated receiver (10) for detecting terahertz radiation (R) reflected at a test object (2; 2a),

   - a first collimator-focussing arrangement (4)

   - having collimator-focussing elements (14, 15, 16, 17) for transforming the emitted terahertz radiation (S) into collimated radiation and for focussing the reflected terahertz radiation (R) onto the beam point (SP),

   - wherein the collimator-focussing elements (14, 15, 16, 17) are arranged in such a way that two adjacent collimator-focussing elements (14, 15, 16, 17) enclose an angle (α_KF) of 90° in the x-y plane (E_xy), so that the collimator-focussing elements (14, 15, 16, 17) form a collimator-focussing square (18),

   - wherein a common focal point (B₁) of the collimator-focussing elements (14, 15, 16, 17) in the x-y plane (E_xy) lies in the beam point (SP),

   - a test object receiving area (6) lying in the x-y plane (E_xy) for positioning the test object (2; 2a),

   - at least one mirror arrangement (5; 39)

   - having mirror elements (19, 20, 21, 22; 41, 42, 43, 44) for deflecting the collimated terahertz radiation (S) and the reflected terahertz radiation (R) between the collimator-focussing arrangement (4) and the test object receiving area (6),

   - wherein the mirror elements (19, 20, 21, 22; 41, 42, 43, 44) are arranged in such a way that in each case two mirror elements (19, 20, 21, 22; 41, 42, 43, 44) enclose an angle (α_SE) of 90° in the x-y plane (E_xy), so that the mirror elements (19, 20, 21, 22; 41, 42, 43, 44) form a mirror rectangle (23; 40),

   - wherein mirror surfaces (24, 25, 26, 27) of the mirror rectangle (23; 40) are parallel to one of the collimator-focussing diagonals (28, 29) of the collimator-focussing square (18),

   - wherein the collimator-focussing elements (14, 15, 16, 17) lie within the mirror rectangle (23; 40), and

   - a control unit (7) for evaluating the detected terahertz radiation (R).
2. Measuring device according to Claim 1, characterised in that two adjacent collimator-focussing elements (14, 15, 16, 17) are perpendicular to one another in the x-y plane (E_xy) and, in addition, two adjacent mirror elements (19, 20, 21, 22; 41, 42, 43, 44) are perpendicular to one another in the x-y plane (E_xy).
3. Measuring device according to Claim 1 or 2, characterised in that the collimator-focussing elements (14, 15, 16, 17) are formed identically, in particular in shape and/or size.
4. Measuring device according to any one of the preceding claims, characterised in that the collimator-focussing elements (14, 15, 16, 17) are formed as lenses.
5. Measuring device according to any one of the preceding claims, characterised in that the mirror elements (19, 20, 21, 22) are formed identically, in particular in shape and/or size.
6. Measuring device according to any one of the preceding claims, characterised in that the mirror arrangement (5; 39) is formed in such a way that a first mirror element (19, 20, 21, 22; 41, 42, 43, 44) deflects the collimated radiation (S) onto a second mirror element (19, 20, 21, 22; 41, 42, 43, 44), wherein the second mirror element (19, 20, 21, 22; 41, 42, 43, 44) deflects the radiation (S) onto the test object receiving area (6).
7. Measuring device according to Claim 6, characterised in that the mirror arrangement (5; 39) is formed in such a way that the collimated radiation (S) impinges on the first mirror element (19, 20, 21, 22; 41, 42, 43, 44) and the second mirror element (19, 20, 21, 22; 41, 42, 43, 44) at an angle of incidence (α_EIN) of 45° in each case.
8. Measuring device according to any one of the preceding claims, characterised in that the transmitter-receiver unit (3; 3a) is formed in such a way that the emitted radiation (S) can be rotated about the beam point (SP) in the x-y plane (E_xy).
9. Measuring device according to Claim 8, characterised in that the transmitter-receiver unit (3; 31) is designed in such a way that it can be arranged rotatably about a rotational axis (12) in the beam point (SP).
10. Measuring device according to Claim 8, characterised in that the transmitter-receiver unit (3; 3a) has a rotational mirror (11) which can be rotated about a rotational axis (12) running perpendicular to the x-y plane (E_xy) through the beam point (SP).
11. Measuring device according to Claim 10, characterised in that the rotational mirror (11) is tilted about a tilt angle (α_K) of 45° against the x-y plane (E_xy).
12. Measuring device according to any one of the preceding claims, characterised in that a second collimator-focussing arrangement (37) is arranged in the test object receiving area (6) concentrically to a test object focal point (B₂).
13. Measuring device according to Claim 12, characterised in that the first collimator-focussing arrangement (4) and the second collimator-focussing arrangement (37) are formed identically.
14. Measuring device according to Claim 12 or 13, characterised in that a respective collimator-focussing diagonal (28; 32) of the first collimator-focussing arrangement (4) and of the second collimator-focussing arrangement (37) coincides with a median line (33) of the mirror rectangle (23).
15. Measuring device according to any one of the preceding claims, characterised in that the control unit (6) is designed to measure the test object by means of the terahertz radiation based on the measurement of a delay time of the terahertz radiation which is reflected at boundary layers, e.g. pipe outer wall, pipe inner wall and abutting material layers within the test object (2).
16. Method for measuring test objects (2, 2a), comprising the steps:

    - providing a measuring device (1; 1a; 1b) according to at least one of Claims 1 to 14,

    - positioning a test object (2; 2a) in such a way that its central longitudinal axis (35; 35a) runs through the x-y plane (E_xy) in the test object receiving area (6),

    - emitting terahertz radiation by means of the transmitter (9),

    - collimating the emitted terahertz radiation (S) to transform the emitted terahertz radiation (S) into collimated terahertz radiation by means of the first collimator-focussing arrangement (4),

    - deflecting the collimated terahertz radiation (S) by means of the mirror arrangement (5; 39) to the test object receiving area (6),

    - reflecting the collimated terahertz radiation (S) at the test object (2; 2a),

    - deflecting the reflected terahertz radiation (R) by means of the mirror arrangement (5; 39) in the direction of the receiver (10),

    - focussing the reflected terahertz radiation (R) by means of the first collimator-focussing arrangement (4) in the common focal point (B₁) of the collimator-focussing elements (14, 15, 16, 17),

    - detecting the focussed terahertz radiation (R) by means of the receiver (10) and

    - evaluating the detected terahertz radiation (R).
17. Method according to Claim 16, characterised in that the emitted terahertz radiation (S) rotates about the beam point (SP).
18. Method according to Claim 16 or 17, characterised in that the emitted terahertz radiation (S) and the reflected terahertz radiation (R) at least partly have the same beam path.
19. Method according to any one of Claims 16 or 18, characterised in that a test object (2) consisting of plastic is measured by measuring a delay time of the terahertz radiation which is reflected at boundary layers, in particular at surfaces of the test object (2), e.g. of a pipe outer wall and/or pipe inner wall and/or abutting material layers within the test object (2).

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